The invention is generally related to the use of shackles used to lift and lower equipment and more particularly to a means of releasing the equipment from the shackles.
In the offshore oil and gas industry, it is routinely necessary to lower equipment to the sea floor or to specific levels of structures underwater. Because of the water depths involved, as deep as 5,000 feet or deeper, it is often unsafe and impractical to use divers. At these depths, use of an ROV (Remotely Operated Vehicle) is preferred for underwater operations.
In the past it has been common to use a hydraulic shackle pin release mechanism that enabled shackles to be removed from equipment underwater without substantial outside assistance. The hydraulic release mechanism can be remotely activated by an ROV, thus allowing surface vessels to lower equipment and disengage the attached rigging without the support of divers.
As seen in the prior art drawing of FIG. 1, the hydraulic release shackle link pin is a link pin arrangement that has one side of the link plate connected to a padeye and the other side connected to a sling. This serves the purpose of having a hydraulic pin transfer force from the slings to the padeye. After transfer of load is complete, the hydraulic pins can be activated to release the load and recover the rigging to the surface. These hydraulic plates are operated by ROV's and are suitable for deep water environments. A major downside of the hydraulic link plates is the potential for failure if the device is not hydraulically primed correctly prior to installation. Because of the extreme water pressures at depth, incorrect hydraulic priming has the potential for the pin to succumb to hydrostatic load, thereby retracting the pin back from the padeye and providing the potential for a full release of the load prior to the desired time. As an example, the hydrostatic pressure at 5,000 feet in seawater is approximately 2,222 pounds per square inch. Such a premature full or even partial release of the load can result in damage to or complete loss of the equipment.
Another issue with the hydraulic release mechanism is the potential for leakage which could pose an environmental hazard.